Conformance unit
In OPC UA, a Conformance Unit is the smallest testable requirement in the conformance system: one named capability with defined behaviour that the Compliance Test Tool can pass or fail. Facets group conformance units, Profiles group facets, and every released nodeset ships a documentation CSV naming the conformance units each standard NodeId belongs to.
The unit of testing
A conformance unit is deliberately small: something like handling a specific service parameter combination, or exposing a specific set of nodes with specific semantics. The Compliance Test Tool is organised around them, running scripts per conformance unit and reporting pass, fail or warn. When a lab report says a product failed, it failed named conformance units, not a vague category.
The documentation CSV nobody uses
Every released nodeset in the UA-Nodeset repository ships a *.documentation.csv alongside the NodeSet2 XML. Each row maps a standard NodeId to its specification section and to the conformance units that node belongs to. Strings such as "GPOS Zones;", "RSL SpatialObject AttachPoints;", "UAFX ConnectionManager Base;", "DI SU Software Update;" and "WMTP DeviceConfiguration Calibration Capabilities;" come straight out of those files. It is the cleanest way to see what a conformance unit actually covers, and almost nobody opens it.
Using it in practice
Open the documentation CSV for the companion spec you are implementing and filter by conformance unit. You get, for free, the exact node list that a tester will look for. That turns "implement the machinery model" into a bounded checklist, and it lets you write a purchase specification that names conformance units rather than marketing terms.
Example
Shape of a row in a released *.documentation.csv
NodeId, BrowseName, spec section, conformance units
... , SoftwareUpdate, 8.2, "DI SU Software Update;"
... , Zones, 6.4, "GPOS Zones;"
... , AttachPoints, 7.1, "RSL SpatialObject AttachPoints;"
Files ship next to the NodeSet2 XML in the UA-Nodeset repository,
e.g. Schema/Opc.Ua.NodeSet2.Services.documentation.csv for the core.Defined in: Part 7 - Profiles. Conformance-unit semantics are in section 4.3.
Last verified 7 September 2026 against OPC UA 1.05.07. OPC UA Connect is an educational resource and is not affiliated with the OPC Foundation.